Purification of glyceride oils



Match 1, 1949.

B. H. THURMAN PURIFICATION OF GLYCERIDE OILS Filed July is, 1944 IN VEN TOR.

ATTORNEYS Patented Mar. 1, 1949 PURIFICATION OF GLYCERIDE OILS Benjamin H. Thurman, New York, N. Y., assignor, by mesne assignments, to Benjamin Clayton, Houston, Tex., doing business as Refining, Un-

incorporated Application July 19, 1944, Serial No. 545,694

2 Claims. (Cl. 260-425) This invention relates to the purification of glyceride oils and more particularly to the puri-,

impurities is often necessary prior to placing the same on the market or incorporating itinto edible or other products. For example, substantially completely refined glyceride oils which have been subjected to hydrogenation to harden the same frequently contain small amounts of free fatty acids produced during the hydrogenation operations. Also, oils which have been primarily refined with non-saponifying alkalies; for example, in accordance with the processes disclosed in the patents to Clayton, Nos. 2,249,701 and 2,249,702, granted July 15, 1941, many times contain excess coloring matter and other impurities in small amounts. This is particularly true as to cottonseed oils and other highly colored oils. Non-saponifying alkalies, such as soda ash, adequately remove the free fatty acids and gums, but do not sufficiently remove the color and other residual impurities. Even with light colored oils, such as corn oil, the residual impurities left in the oil after refining with a non-saponifying alkali interfere with water washing. Furthercient in removing the residual impurities fromoils of the type above discussed. Such caustic alkalies precipitate the residual impurities including coloring matter and at the same time pro-- duce small amounts of soap. When such caustic alkalies are employed, difficulty is encountered in securing adequate separation of the precipitated impurities and residual refining agent from the oil. For example, in centrifugal separating operations, three layers instead of two tend to be produced in the centrifugal separator. The lighter of these layers is the purified oil and the heavier layer is the aqueous phase containing precipitated impurities, water and excess reagent in solution. An intermediate layer made up largely of soap rendered insoluble in the aqueous phase by the excess reagent, however, tends to form, and as the layers are not clearly defined, it is impossible to adjust the centrifugal separator to produce a clean separation of purified 'oil from the intermediate layer. That is to say, a portion of the intermediate layer containing soap will either be discharged with the oil to prevent the production of a pure oil or a substantial quantity of the oil will be discharged with the heavy efiluent resulting in a substantial loss of the valuable oil. The phenomena of forming three layers in the centrifugal is referred to in the art as stratification.

One Way of preventing such stratification is to employ an extremely dilute aqueous solution of the refining reagent, in which case the soap stays in solution or suspension in the aqueous phase. Other difiiculties are, however, encountered when dilute reagents are employed. Such dilute reagents usually do not react sufficiently with the impurities in the oil and in thecase of highly colored oils do not sufficiently reduce the color. They also result in valuable oil being emulsified into the aqueous phase so as to prevent its separation therefrom. Because of the large volume of aqueous phase produced when using dilute reagents, substantial losses of valuable oil are caused. As disclosed in the application to Clayton, Ser. No. 483,953, filed April 21, 1943, now patent Serial No. 2,412.251, issued December 10, 1946, it is possible to first employ a concentrated aqueous alkaline refining agent and then dilute the resulting mixture just prior to introducing the same into the centrifugal superator or within the separator itself prior to completion of the separation therein, the latter step being preferable. By this operation, the aqueous phase is sufiiciently diluted so that the soap remains in solution or suspension therein, but substantially no valuable oil is emulsified into the aqueous phase. An important factor resulting in stratification in the centrifugal separator appears to be the substantial absence of gums in oils of the type contemplated in the present invention. The presence of material amounts of gums in the oil apparently emulsifies or otherwise keeps the soap in suspension in the aqueous phase Without causing material emulsification of oil into the aqueous phase.

In accordance with the present invention, it has been discovered that the stratification above discussed as occurring in the centrifugal separator is a function of time as well as a function of Thus, an'alkaline refining reagent of sufficient concentration to purify the oil and prevent losses of purified oil by emulsification into the aqueous phase can be, employed, and if the time of subjection of the mixture to the action of centrifugal force in the centrifugal is made sufficiently short, the

- amounts only of precipitated impurities.

the aqueous phasecontaining the impurities is 'quickly separated from the oil, and if substantial- ,ly immediately discharged from the separator Centrifugal separators, in general, are designed .for an upper maximum rated capacity. For

example, the most widely used commercial centrifugal separators have a maximum rated capacity of approximately 1,000 pounds of'mixture per hour, .the mixture referred to being the mixture resulting from treating glyceride oils with an alkali refining reagent. Thereare also available large-size commercial centrifugals, most of which have a rated capacity for the mixture above referred to of approximately 5,000 pounds per hour.

When purifying oils of the type above discussed, it has been found possible to employ aqueous alkaline refining reagents of sufficient concentration to purify the oil or prevent the emulsions above referred to and then deliver the resulting mixture containing precipitated impurities including soap to the centrifugal separator at a rate sufficiently high to prevent the stratification imculty above described. The most advantageous procedure is to use just sufficient concentration to cause adequate precipitation of impurities or to prevent emulsifying of the oil into the aqueous phase. This concentration will, in general, result in Stratification under conventional operating conditions for centrifugal separators. By substantially increasing the throughput, it has been found, contrary to the teachings of the. art, that separation is materially improved particularly with respect to the absence of stratification. In many cases, it is found-that an I increase of throughput of approximately 25% will eliminate the Stratification and produce substantially complete separation into'two efliuentsfo'n'e being the soap free purified oil and the other the aqueousphase containing 'water, excess reagent and precipitated impurities. Howeven-in some 4 an improved process of preventing stratification and attendant separation difliculties during centrifugal separation of impurities and excess reagent from a mixture resulting from mixing an aqueous alkaline refining reagent with a glyceride oil containing small amounts only of impurities.

A still further object of the invention is to provide a process of purifying a glyceride oil containing small amounts of impurities with an aqueous alkali reagent in which separation difliculties during centrifugal separation ofexcess reagent and precipitated impurities from the oil are prevented by providing insuflicient time during such separation to produce Stratification of the mixture being separated.

The process, of the present invention is preferably carried out as ,a continuous operation, a suitable apparatus for carrying out the process being shown in the attached drawing. Beferring particularly to the drawing, a source of supply for the oil to be purified is shown as a tank I0 from which the oil may be withdrawn by a proportioning pump I I and passed through a heat exchange device I2, shown as a coil I3 positioned in a casing I I, to a mixer I6. Refining reagent may be withdrawn from a tank H by means of aproportioning pump I8 and forced thereby through a heat exchanger I9 shown as a coil 2| positioned in the casing 22. The refining reagent may also be forced by the pump I 8 into the mixer I6 where it is mixed with thenoil from the tank Ill. The mixer I6 is preferably of the flow type disclosed in the patent to Thurman No. 2,142,062, granted Dec-27, 1938, but may be any suitable type of mixing device which thoroughly brings the refining agent into contact with all portions of the oil. The pumps II and I8 may be driven by a variable speed motor 23 with a variable speed device 24 positioned between the motor 23 and the pump I8 for the refining reagent. It will be apparent that the pumps I I and I8, with the motor 23 and variable speed device 24, constitute a proportioning device. The specific proportioning device shown is byway of example only, and any "other suitable type of proportioning device, for

example, that shown in the patent to Thurman 7 above referred to may be employed.

In most cases, the proportioning device will cases, it may be necessary to increase this throughpu'tjby 100%, the average throughput necessary to prevent stratification'usually being about 40% greater than the rated capacity of the centrifugal separator. It is probable that this increased throughput can be accomplished by reason of the ease with which a relatively concentrated causticalkali solution can be separated from glyceride oils in the presence of small Thus,

' vide an improved process of purifying glyceride oilscontaining small amounts of impurities.

Another object of the invention is to provide an improved process of purifying glyceride oils containing small amountsofimpurities in which stratification and separation 'difliculties during centrifugal separation are prevented'.'-,

A further object of the invention are provide the mixer I6 through a third heat exchange device 26 shownas a coil 21 positioned in a casing '28 to the centrifugal separator 29. Depending upon the type of oil being treated, either preheating .of the oil and alkali in the heat exchangers I4 and I9 can be employed or the resulting mixture can be heated in the heat exchanger 26, or both heating steps may be employed. With certain oils, preheating prior to mixing is found to be more advantageous while-with other oils cold mixing followed by heating aftermixing produces betterresults'. With other oils, ithas'even been found desirable to preheat to a relatively high temperature, for example, temperatures between 3 upon'whether heating or cooling is to be eflected.

140 and 160 F. and mix at these temperatures and then cool to a lower temperature, for example to F., in the heat exchanger 26 prior to separation, It will be apparent that any desired heating or cooling medium can be circulated through the casings 14, 22, and 28 of the heat exchangers I2, I9, and 26, respectively, depending In general, separation in the centrifugal sep- -arator will be carried onbetween temperatures of '100 and F., depending upon the nature .of the oil being treated. With viscous oils, it is frequently necessary to use temperatures in the upper portions of saidrange, while with other oils, lower temperatures provide best separation. Elevated. temperatures assist in the separation as they render the soap more soluble in the aqueous phase, reduce the viscosity of the oil, and tend to break any emulsion of oil in the aqueous phase. The major factor enabling adequate separation without substantial contamination of the oil phase with soap or loss of valuable oil in the aqueous phase is, however, the increased throughput contemplated by the present invention. This increased throughput can be accomplishedby employing proportioning pumps and mixing devices as well as heat exchangers which are of suiiicient capacity to deliver a mixture to the centrifugal 29 which is substantially above its rated capacity. In installations in which a plurality of centrifugal separators are concurrently fed from a single mixing device, a lesser'number of centrifugals can be employed than would be expected from their rated capacities, thus decreasing the size and expense of an installation designed to purify oils having small amounts of impurities.

The concentration of the aqueous alkali refining reagent will depend largely upon that necessary to prevent emulsifioation of oil into the aqueous phase, This concentration will usually 'fall between 16 and 50 B., but in occasional instances the concentration may be as low as 10 B. A substantial excess of refining reagent is generally necessary to produce adequate purification of the oil and prevent emulsification of oil in the aqueous phase so that the aqueous phase being separated contains this excess in solution. When refining reagents of suiiicient amounts and concentration to adequately purify'the oil are employed, the excess reagent salts out the soap present in the mixture in the absence of substantial amounts of gums, thus causing the stratification difiiculties discussed above. By maintaining the throughput of the centrifugal separators at a rate sufliciently high that the soap is carried out of the separators before it can separate from the main layer of aqueous material, this stratification can be prevented. That is, the aqueous phase carrying the soap appears to first separate from the oil and thereafter the soap separates from the aqueous phase and tends to mix with the oil phase. By discharging the aqueous phase after separation from the oil and prior to separation of the soap therefrom, a clean separation between oil and aqueous phase including soap is accomplished.

While I have disclosed the preferred embodiment of my invention, it is understood that'the phase, whereby the resulting mixture first separates into an oil phase and .an aqueous phase in a continuous centrifugal separator and then an intermediate soap phase tends to separate from said aqueous phase and partially mix with said oil phase, subjecting said mixture to said continuous centrifugal separation, and discharging said aqueous phase from said continuous separator substantially as soon as it separates from said oil phase and prior to substantial separation of said intermediate soap phase from said aqueous phase.

2. The method of puriiyingglyceride oils which are substantially free of gums and which contain small amounts only of impurities, which process comprises, admixing with said oil an. aqueous caustic alkali refining agent having a concentration between 10 and 50 B. and in just sufiicient amounts to produce separation of impurities from the oil as part of an aqueous phase during continuous centrifugal separation of the mixture, the concentration of said agent being suflicient to prevent emulsification of the oil into said aqueous phase, whereby the resulting mixture first separates into an oil phase and an aqueous phase in a continuous centrifugal separator and then an intermediate soap phase tends to separate from said aqueous phase and partially mix with said oil phase, subjectin said mixture to said continudetails thereof may be varied within the scope of the following claims.

I claim: I 1. ,The method of purifying glyceride oils which are substantially free of gums and which contain small amounts only of impurities, which process ous centrifugal separation, and supplying said mixture to said continuous centrifugal separator at a rate sufficient to discharge said aqueous phase from said separator substantially as soon as it separates from said oil phase and prior to substantial separation of said intermediate phase from said aqueous phase.

BENJAMIN H. THURMAN.

' REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain 1888 

